This disclosure relates generally to fabrication systems and methods for assembling structures using a combination of composite materials and structural metal material, and more specifically to drilling systems and methods for preparing composite material and substrate materials for assembly.
The structural performance advantages of composites, such as carbon fiber epoxy and graphite bismaleimide (BMI) materials, are widely known in the aerospace industry. Aircraft designers have been attracted to composites because of their superior stiffness, strength, and radar absorbing capabilities, for example. As more advanced materials and a wider variety of material forms have become available, aerospace usage of composites has increased.
When using fasteners to attach composite skins to metal substrates, coaxial holes must be drilled in both the skin and an underlying metal substrate. In some cases “interference-fit” fasteners are used requiring the coaxial holes to be of different diameters in each of the skin and the substrate. Conventionally, this necessitates separation of skin and substrate during drilling so that separate drilling operations can be carried out on each. The skin and substrate are subsequently assembled to one another and joined with the fastener.
In other cases, the hole diameter may be the same in each material, but because the skin and substrate may require different drill speed and feed rates, efficient drilling of the holes remains elusive.